Air conditioner compressors are commonly provided with a pressure cutoff switch for turning the compressor off when a predetermined pressure is reached. In other embodiments, a thermostat is placed in the plenum chamber to sense temperature and, at a predetermined temperature, it directly shuts off the compressor motor. Both the pressure cutoff and the thermostat cutoff cycles the compressor "off" during high pressure and high temperature conditions and back to the "on" position when the pressure or temperature is again at normal level.
In the event of a malfunction, such as an electrical failure or externally applied heat, either the thermal cutoff or the pressure cutoff may not turn the compressor off. The pressure will then continue to build and could result in an explosion. To prevent such an explosion, it is common to provide a pressure relief valve for venting the pressure when it exceeds a predetermined value.
In commonly assigned U.S. Pat. No. 4,948,931, a pressure relief valve is disclosed in which a snap disc, capable of assuming opposite bowed positions, will snap to a reverse bowed configuration and cause a diaphragm to be ruptured by a pin. The pressure will then be vented through the interior of the housing to the vent opening. In such case, when the problem is corrected, the pressure relief valve has to be replaced.
In a first embodiment, the present invention overcomes the disadvantages of the prior art by providing a simple snap disc that is snappable between opposite bowed positions. In one position, the snap disc seals a vent orifice in a chamber such that when the temperature in the chamber reaches a predetermined amount, the snap disc is snapped to the opposite bowed position to uncover the vent orifice and vent the pressure in the chamber. When the temperature returns to normal, the snap disc is snapped back to the initial bowed position thus again sealing the chamber and allowing pressure to exist. The vent orifice has a valve seat and the snap disc has a matching shape with a surface substantially in the center thereof for matching the arcuate valve seat to completely seal the orifice in the first bowed position. While there are different types of matching valve seats and snap discs, for ease of explanation and representation in the drawings, an arcuate shape will be used and shown. However, it should be noted that the term "arcuate" is intended to cover any matching seals including simple square shoulders sealed around and over the orifice of the valve seat. In this embodiment, there is at least one orifice in the snap disc in the area surrounding the arcuate convex sealing surface to allow pressure in the enclosed chamber to be vented through the vent orifice when the snap disc is in the opposite bowed position.
In a second embodiment, the arcuate convex sealing surface is an insert in the snap disc for sealing the orifice and the insert may be a rivet-like structure whose head seals the vent orifice or a polymeric structure with a convex head that seals the vent orifice.
In yet another embodiment, the vent orifice includes a polymeric valve seat in the shape of a truncated cone and the snap disc is saucer shaped with a flat surface matching the truncated cone surface to completely seal the vent orifice in the first bowed position of the snap disc.
In still another embodiment, at least one recess is formed in the periphery of the snap disc to allow pressure in the enclosed chamber to be vented through the recess and the vent orifice when the snap disc is in the opposite bowed position.
Also, in still another embodiment, an opening is formed in the chamber under the periphery of the snap disc in at least one area to allow pressure in the enclosed chamber to be vented through the opening and the vent orifice when the snap disc is in the opposite bowed position.
In the embodiments just discussed, the snap disc is installed in a valve having a spatial orientation such that gravity causes the snap disc to settle under its own weight onto the vent orifice so that the orifice can be sealed. To ensure a positive seal or to use the snap disc in a device in which the spatial orientation of the snap disc is such that it cannot be pulled by gravity onto the vent orifice, a biasing mechanism is associated with the snap disc to forcibly orient it in sealing relationship with the vent orifice in the first bowed position. In one of these embodiments, the biasing mechanism is a resilient foam washer mounted between the chamber and the snap disc such that when the snap disc reverts to the first bowed position from the second bowed position, the resilient foam washer forces the snap disc into sealing relationship with the vent orifice.
In another embodiment, the biasing mechanism is a coil spring mounted between the chamber and the snap disc such that when the snap disc reverts to the first bowed position from the second bowed position, the coil spring forces the snap disc into sealing relationship with the orifice.
Where the vent orifice has a concave surface and the snap disc has a mating concave surface such that the mating surfaces seal the orifice in the first bowed position, the biasing mechanism can be a spring with an axial extension mounted between the chamber and the snap disc with the axial extension engaging the concave surface of the disc such that when the snap disc reverts to the first bowed position from the second bowed position, the spring with axial extension forces the snap disc into sealing relationship with the orifice.
Thus, it is an object of the present invention to provide a thermally responsive pressure relief valve for mounting in an enclosed chamber and which has a vent orifice and a snap disc being snappable between opposite bowed positions with the snap disc sealing the vent orifice in a first bowed position such that when the temperature in the chamber reaches a predetermined amount, the snap disc is snapped to the opposite bowed position to uncover the orifice and vent the pressure in the chamber.
It is yet another object of the present invention to provide a pressure relief valve with a snap disc having a saucer shape with an arcuate convex surface substantially in the center thereof for matching an arcuate valve seat to completely seal the orifice in the first bowed position of the disc.
It is also an object of the present invention to provide orifices in a valve snap disc in an area surrounding an arcuate convex surface that seals the vent orifice to allow pressure in the enclosed chamber to be vented through the vent orifice when the snap disc is in the opposite bowed position.
It is still another object of the present invention to provide a relief valve with a snap disc having an arcuate convex surface formed in an insert of the snap disc for sealing a vent orifice.
It is also an object of the present invention to provide a vent orifice formed of a polymeric valve seat in the shape of a truncated cone with a snap disc being saucer shaped with a substantially flat surface matching the truncated cone surface to completely seal the vent orifice in the first bowed position of the snap disc.
It is yet another object of the present invention to provide a relief valve with at least one recess in the periphery of a snap disc to allow pressure in an enclosed chamber to be vented through a vent orifice when the snap disc is in the opposite bowed position.
It is also another object of the present invention to provide a relief valve with a vent orifice in a chamber being sealed by a snap disc in a first bowed position and including an opening in the chamber under the periphery of the snap disc to allow pressure in the enclosed chamber to be vented through the chamber opening and the vent orifice when the snap disc is in the opposite bowed position.
It is still another object of the present invention to provide a thermally responsive pressure relief valve wherein a snap disc is mounted in a chamber of the relief valve in a spatial relationship such that gravity orients the snap disc in sealing relationship with the vent orifice when the snap disc is in the first bowed position.
It is also another object of the present invention to provide a thermally responsive pressure relief valve in which a biasing mechanism is associated with a snap disc to forcibly orient snap disc in sealing relationship with a vent orifice when the snap disc is in the first bowed position regardless of the spatial orientation of the snap disc and the chamber. The biasing mechanism may be a resilient foam washer, a coil spring or a spring with an axial extension, any one of which would be mounted between the chamber and the snap disc such that when the snap disc reverts to the first bowed position from the second position, the biasing mechanism forces the snap disc into sealing relationship with the orifice.